Weightbearing Cone-Beam Computed Tomography of Acute Ankle Syndesmosis Injuries.

Syndesmotic injuries are common, but only a subset of these injuries are unstable. A noninvasive tool for identifying instability would aid in the selection of patients for surgery. Weightbearing computed tomography (CT) data have been reported for healthy patients, but there are limited data on unstable syndesmoses. We evaluated the syndesmotic area of arthroscopically proven unstable ankles after acute injury. This is a prospective comparative study of consecutive patients recruited to a weightbearing CT database. Thirty-nine patients were included for analysis with arthroscopically proven unstable syndesmoses and an uninjured contralateral ankle. The syndesmosis area was measured for both ankles, in non-weightbearing and weightbearing positions, and compared. Syndesmosis area of the unstable ankle was significantly greater than the uninjured ankle of the same patient, by a mean of 22.9 ± 10.5 mm2. This was a significantly greater difference than that observed with non-weightbearing CT (9.8 ± 10.2 mm2, p < .001). Dynamic change in area, from non-weightbearing to weightbearing, of the unstable ankle (13.7% [16.6 ± 9.9 mm2]) was significantly greater than that of the uninjured ankle (3.1% [3.4 ± 6.7 mm2], p < .001). The intraobserver and interobserver correlations were good with intraclass correlation coefficients of 0.983 and 0.970, respectively. Weightbearing CT demonstrated significantly greater diastasis in unstable ankles than did conventional non-weightbearing CT. Syndesmosis area measurement was reliable and reproducible. Dynamic change in area and weightbearing comparison with the contralateral uninjured ankle are 2 parameters that may prove useful in the future for predicting syndesmotic instability.